This invention relates to a method for producing, through extrusion, an anisotropic magnet with high energy product.
It is known to produce an anisotropic permanent magnet through an extrusion process whereby a body charge of composition from which the magnet is to be produced is placed in a container, heated and extruded within the container to compact the body charge to substantially full density. U.S. Pat. No. 4,915,891 (Chandhok et al.) describes such a method.
In practice, however, this method has suffered from disadvantages which have precluded use of the resulting permanent magnets for commercial purposes. More specifically, while the prior art is intended to produce a permanent magnet having anisotropic magnetic properties along the axis thereof, in practice the prior art process produces permanent magnets with magnetization vectors that are random in the plane perpendicular to the extrusion direction and, therefore, the prior art is not able to produce a true anisotropic magnet (i.e., magnets with asymmetric magnetic properties along the axis thereof), through extrusion, with high energy product.
As described in Chandhok et al., it is known to produce a permanent magnet with anisotropic properties through an extrusion process. In particular, it is known to employ a rectangular extrusion die in connection with an extrusion process whereby a body charge of a composition from which the magnet is to be produced is placed in a cylindrical container, the container and body charge are heated and the container and body charge are extruded on a non-uniform basis to a substantially full density. In particular, an extrusion ratio within the range of 1.5:1 to 50:1 is used, together with extrusion temperatures within the range of 500xc2x0 to 1500xc2x0 C. Such non-uniform extrusion, as described in the prior art, occurs across all dimensions of the container and body charge.
By way of specific example, Chandhok et al. describes a 3xe2x85x9 inch diameter mild steel can which, after insertion of the body charge, is extruded to a rectangular shape with dimensions of 1.66 inches (w)xc3x970.55 inches (T) at an average extrusion ratio of 8.4 to 1. While such an extrusion process produces asymmetric magnetic properties which vary at the transverses measured along the two dimensions, random magnetization vectors also exist. As a result of such random magnetization vectors, the resulting magnet does not have a high energy product.
It is the purpose of the present invention, therefore, to provide an improved method for producing permanent magnets with anisotropic properties through an extrusion process.
In particular, it is the object of this invention to provide a method for producing an anisotropic magnet body with high energy product through an extrusion process wherein optimum die shapes, extrusion ratios and extrusion temperatures are used. In particular, in the preferred embodiment of this invention, the container and the charge are extruded to a noncircular cross-sectioned shape, such as a rectangle, with one dimension being held substantially constant during extrusion.